Certified Passive House Designer / Consultant key terms

Annual useful heat delivered to the building per treated floor area, expressed in kWh/(m²a). It excludes domestic hot water and is the headline Passive House metric, capped at 15 kWh/(m²a) in cool-temperate climates.

The reference area used in PHPP, measured inside the thermal envelope and adjusted by a utilisation factor for rooms with unusual ceiling heights or uses. All area-normalised results depend on it, so errors propagate through every indicator.

The peak heat output in watts needed to hold the indoor setpoint on the design cold day. In Passive House it is typically 10 W/m² or less, which allows the ventilation supply air alone to carry the heat.

Total energy consumed at source, including extraction, conversion and delivery losses, divided by treated floor area. PHPP reports it as renewable (PER) and non-renewable (PEne) variants, with the certification limit applied to PER.

A multiplier converting delivered energy for a given carrier into source energy, accounting for grid or supply-chain losses. Factors differ by country and carrier, so the same building can pass in one national dataset and fail in another.

The continuous boundary separating conditioned from unconditioned space, formed by insulation, airtightness layer, windows and doors. Its position determines the treated floor area, the heat loss area and where thermal bridges must be interrupted.

Steady-state heat flow through one square metre of construction per kelvin of temperature difference, in W/(m²K). Lower values mean better insulation; opaque Passive House envelopes typically sit between 0.10 and 0.15 W/(m²K).

A localised path where heat flows more readily than through the surrounding construction, caused by geometry, material penetration or gaps in insulation. Each bridge is quantified by a linear or point heat loss coefficient and added to the transmission losses.

The linear thermal transmittance of a junction, in W/(mK), describing heat loss per metre of junction length beyond the losses already counted in the adjacent U-values. It is multiplied by junction length and temperature difference in the PHPP.

A design approach in which all junctions are detailed so that insulation and airtightness layers run continuously, keeping Psi-values at or below about 0.01 W/(mK). This allows the certification calculation to assume no penalty for junctions.

The continuous, sealed plane in the building fabric that stops uncontrolled air movement through the envelope. It is usually a membrane, plaster or board, and must be joined to window frames, penetrations and floor slabs without breaks.

Air change rate per hour at 50 pascals of pressure difference, referenced to the building volume. Passive House certification requires 0.6 h⁻¹ or less, verified by measurement rather than by design assumption.

A pressurisation test using a calibrated fan to measure envelope leakage at a series of pressure differences. Results feed the PHPP and the certification decision; a failed test usually means locating and sealing leaks before retesting.

The whole-window heat transfer coefficient including glazing, frame and spacer effects, in W/(m²K). Passive House certification typically requires around 0.80 W/(m²K) or better for the installed window.

The fraction of incident solar radiation that enters the room as useful heat gain, combining direct transmission and inward secondary radiation. Higher values reduce heating demand but raise overheating risk, so the choice is climate and orientation dependent.

Useful heat from sunlight passing through glazing into the building, counted in PHPP month by month with shading reductions. They offset heating demand in winter and are the main driver of overheating in summer.

A multiplier between 0 and 1 reducing solar gains to account for external obstructions, overhangs, reveals and movable shading. It is applied in the PHPP and must match the shading actually installed and commissioned.

Fitting windows so the frame sits within the insulation layer, with a sealed connection to the airtightness layer and insulated reveals. This keeps the installation Psi-value near zero and avoids cold frame edges and surface condensation.

The energy needed to warm incoming outdoor air to indoor temperature, reduced by heat recovery. In PHPP it is calculated from air change rate, heat recovery efficiency, frost protection and any infiltration through the envelope.

The share of sensible heat in extract air transferred to incoming supply air, usually 75–90 % in certified units. It is measured under standard conditions and must be corrected for unbalanced flows and frost protection in the PHPP.

A balanced supply and extract system that continuously delivers filtered outdoor air and recovers heat from exhaust air. It provides fresh air without relying on window opening and is a core Passive House component.

Covering the whole space heating load by warming the ventilation supply air, feasible when the heating load stays around 10 W/m². It removes the need for radiators but limits supply temperature and requires careful room-by-room air distribution.

A duct-mounted heater after the heat recovery unit that raises supply air to the required temperature. It may be a hot-water coil, electric element or heat pump condenser, and its output defines the achievable air heating capacity.

The total resistance of the air distribution system, in pascals, from filters, ducts, bends and valves. Low pressure drop keeps fan power and electricity use small, which matters because fan energy counts in primary energy.

The percentage of hours in a year when indoor operative temperature exceeds 25 °C, assessed in PHPP. The Passive House criterion limits this to 10 % of hours, and it is the main check on glazing area, shading and thermal mass.

Flushing the building with cool night air, by opening windows or running bypassed ventilation, to remove stored heat from mass. It reduces daytime overheating in summer and is often needed to meet the overheating criterion.

The ratio of useful heat delivered over a year to the electricity consumed by the heat pump, including source and distribution auxiliaries. It drives both primary energy and CO₂ results, so a poor installation can fail an otherwise good envelope.

Heat lost from pipes, cylinders and circulation loops between the generator and the tap, which can exceed the useful hot water energy in poorly planned systems. Short pipe runs, insulation and demand-controlled circulation keep losses low.

The method that prevents ice forming in the heat exchanger during cold weather, such as preheating supply air, a bypass, or temporary imbalance. The chosen strategy affects calculated heat recovery efficiency and ventilation heat loss.

The structured process of adjusting, measuring and documenting building services so they perform as designed, including air flow balancing, control checks and functional tests. Certification expects evidence of completed commissioning before handover.

Adjusting dampers and valves so each room receives its design supply or extract volume within tolerance, while keeping the system near balanced pressure. It protects heat recovery efficiency, indoor air quality and the calculated energy balance.

Independent verification by an accredited certifier that a building meets the criteria for heating demand, primary energy, airtightness and overheating, based on submitted PHPP and evidence. It is distinct from the designer's own credential.

The Passive House Planning Package, a validated spreadsheet tool that calculates heating demand, loads, primary energy and summer comfort from building and systems data. Its verification dataset must match the built building for certification.

The sensible heat that must be removed to keep indoor temperatures acceptable, after solar and internal gains and any passive cooling. It is calculated alongside overheating metrics and informs whether active cooling is needed.

Heat released inside the building by occupants, lighting and appliances, estimated from floor area and occupancy assumptions. They reduce winter heating demand but contribute to summer overheating, so assumptions must be consistent and documented.